SELECTION FOR CHANGES IN THE INCIDENCE OF WING DIMORPHISM IN GRYLLUS-FIRMUS

Previous studies suggested that in the cricket Gryllus firmus the heritability of wing dimorphism is approximately 0·65. This estimate was based on a full sib analysis and hence may be confounded by non additive effects. To confirm this estimate a selection experiment was undertaken, lines being selected for increased and decreased incidence of macroptery. The response to selection was asymmetric, response for decreased percentage macroptery being faster than that for increased proportion macroptery. The realized heritability in the “up” line was approximately 0·25, and in the “down” line approximately 0·95, the mean across all lines being 0-6: This agrees very well with the estimate of 0·67 obtained from a full sib analysis. Two possible reasons for the asymmetric response are suggested. In the related cricket species, Gryllus rubens, the genes controlling wing morph appear to be on the sex chromosome while in G. firmus no sex linkage is evident. A new method of estimating realised heritability for threshold traits is presented. © 1990, The Genetical Society of Great Britain.